Participation in a cardiac rehabilitation program is associated with reduced cardiovascular and all-cause mortality. While cardiac rehabilitation is known to have a favorable effect on lipids and physical fitness, the actual mechanisms responsible for the reduction in cardiovascular events and all-cause mortality is unknown. One potential factor is improved endothelial function. If cardiac rehabilitation can improve the vasodilatory capacity of the endothelium, this could provide important new data regarding cardioprotective mechanisms. Our hypotheses are that 1) participation in a cardiac rehabilitation program will be associated with improved endothelial vasodilation, as assessed by brachial artery ultrasound; and 2) such improvement will correlate with improvements in the physiologic parameters studied (cardiovascular fitness, body composition, lipids, performance-related disability). We plan to use brachial artery ultrasound to noninvasively assess endothelial response to flow mediated dilation in participants in the Cardiovascular Health and Activity Maintenance Program (CHAMP). The CHAMP study will compare the effects of a standard 3-month center-based exercise program with a 12-month lifestyle intervention program on physiologic parameters and on health-related quality of life in approximately 160 men and women candidates for cardiac rehabilitation. Participants will be enrolled over a 4-year period, and each participant will be followed for one year. For each subject, brachial artery ultrasound will be performed at entry into the study, after 3 months in the program, and after 1 year in the program.